Abstract
Current studies of cross-sectional observation of live body using computed tomography (CT) have progressed from observation of subcutaneous adipose tissue to that of all body composition. Recently, the emphasis of CT study has been on each muscle belly. To clarify basic movement of the upper limb, I used CT to measure cross-sectional area of each muscle belly in the proximal third of the forearm of 104 humans (49 males, 55 females) and analyzed the muscles according to body type, size of total forearm cross-sectional area and age. The following results were obtained: (1) The muscles having the largest cross-sectional area are M. flexor carpi radialis, M. flexor digitorum superficialis and M. pronator teres. There is no difference between the sexes in this order of cross-sectional area. (2) Analysis by body type showed that each muscle area increases in size in the order of A-C-D, but the ratios of the areas are larger for M. flexor carpi radialis and M. extensor carpi radialis brevis. (3) Increase of each muscle area follows the increase of the total forearm cross-sectional area. It appears that in males development of muscles relating flexion-extension, and radial abduction of the wrist and extension of the digits is more marked, and in females development of muscles related to wrist flexion and elbow flexion is more marked. (4) In analysis by age, the decade in which muscle cross-section area is maximed for most persons is 30-39 years in males and 50-59 years in females. There are no difference between males and females in tendency of muscles to atrophy. (5) There seems to be differences between the two sexes in functions of the forearm muscles.
